This invention relates, in general, to skin preparations, and in particular to a new and useful self dosing preparation which releases one or more active ingredients onto the skin after exposure to the sun or other environmental condition. The active ingredient may include a sunscreen having a UV absorption effect or another skin preparation that is maintained or which increases with exposure to solar radiation. The invention is also generally concerned with creams or lotions containing these preparations as well as various cosmetic compositions containing self dosing sunscreens and/or other skin preparations containing self dosing ingredients such as, but not limited to, fragrances, antiperspirants, dyes, cooling/warming agents, flavors, insect repellents, antibacterial agents, hair conditioners and self tanning agents.
Erythema or xe2x80x9csunburnxe2x80x9d is the direct consequence of exposure of the skin to solar or sun radiation, and particularly the part of the spectrum in the range of 280 to 320 nanometers or UVB, also known as the erythematosus part of the solar spectrum. Furthermore, this part of the spectrum has sufficient energy per photon (between 3.8 to 4.4 electron volts) to cause ionization of organic molecules, including DNA, and is thus considered to be mutagenic, and thus, it is believed that exposure to UVB is a major causal contributor to basal cell carcinoma.
Over the years there have been a number of compounds identified and developed for incorporation in suntan lotions that absorb in the range of 280 to 320 nanometers. Such compounds also require, however, additional properties. It is desired that they transmit some of the solar radiation in the 320 to 400 nanometers range (UVA) in order to enhance tanning. These compounds also must be compatible with carriers and other ingredients in suntan lotions and creams as well as in other cosmetic preparations, such as, but not limited to, base creams, lipsticks and make up preparations. Such compounds also must be non-odorous and be nontoxic and dermatologically compatible.
One can divide topical UV blocking compounds into essentially two classes, organic compounds and inorganic compounds.
Typically, inorganic compound based sunscreens and suntan lotions are formulated within creams and lotions and include fine dispersion of a number of inorganic minerals like kaolin and chalk, or oxides such as titanium dioxide and zinc oxide. These inorganic sun screens have a number of aesthetic as well as health problems related with their use. When applied, they form a white layer which is objectionable to most users. Furthermore, the fine particles of these inorganic materials have a tendency to be lodged in hair follicles resulting in inflammation. Cases of sweat gland inflammation due to occlusion have been reported as well. Furthermore, these inorganic based sunscreens re-liquify when mixed with the wearer""s perspiration and have a tendency to soil the wearer""s garments and are thus objectionable for that reason as well.
Mitchnick et al. in U.S. Pat. No. 5,733,531 suggest to remedy these problems by encapsulating the oxides or pigments into spherical microcapsules having a diameter as large as 100 microns and as small as 0.01 micron. However, it is quite clear that in such an arrangement, when the particles are on the xe2x80x9chigh sidexe2x80x9d of the proposed dimensions (at or near 100 microns) in interstitial light diffusion will cause UVB to reach the epidermis, and in the lower end of the proposed range, the entire microsphere will have a tendency to lodge itself into hair follicles and sweat glands as do the traditional inorganic sunscreen agents. Furthermore, large microcapsules will have a tendency to break and discharge their content (sub-micron sized inorganic oxides) resulting in the same problems cited above.
Representative organic compounds that have been found to possess desired UVB blocking or absorption properties, are typically aromatic compounds, such as derivatives of para-aminobenzoic acid (PABA), PABA esters (glyveryl PABA), amyldimethyl PABA, octyldimethyl PABA and 2-ethylhexyl-paradiethylamino benzoate. These are just a few of the many examples of the PABA type active ingredients in suntan lotions. Benzophenones (Escalol 567), oxybenzone such as 2-hydroxy-4-methoxy benzophenone as well as sulisobenzone, have been used as active ingredients in sunscreen preparations as well. Cinnamates, such as octyl-methoxy-cinnamate (also known as Escalol 557 or Parsol MCX or cinoxate) are also used in this fashion. Salicylates such as homomethyl salicylate have also been used as well as anthranilates such as methyl anthranilate. These compounds are in no way exclusive and many other aromatic compounds have been used over the years as UV blocking agents in suntan lotions and other cosmetic preparations.
One of the shortcomings common to many of these organic UVB absorbing compounds is that relatively large concentrations of these blocking agents must be used to achieve the desired xe2x80x9cProtection Indexxe2x80x9d or PI. The PI is defined as the ratio of the irradiation time required to reach the erythematogenic threshold with the UV screen divided by the irradiation time required to reach the erythematogenic threshold without the UV screen. Naturally, the higher the index, the better is the blocking action of the UV screening agent used. Another shortcoming of most of the existing compounds is believed to be rooted in the fact that the active agents in most sunscreens are relatively small molecules and in time, part of these are absorbed into the epidermis and lose some of their sun blocking action. This require that the user frequently reapply the sunscreen formula to exposed portions of the body, so as to avoid sunburns or erythema.
U.S. Pat. Nos. 3,980,617; 4,107,290 and 4,233,430 to Jacket et al. disclose attempts to overcome these problems by fixing the UV absorbing moieties on certain macromolecular polymers through an acrylamino group replacing hydrogen or other radicals on the main polymer carbon chain. This polymeric structure which has a dangling carbon-carbon bond, is itself subject to UV degradation, however.
Cosmetics and suntan lotions that contains micro-encapsulated ingredients, including UV blocking ingredients have been described before, for instance, by Noda et al. in U.S. Pat. No. 5,089,269. Neither this patent nor any of the prior art the inventors are aware of provide for microcapsules that act as a reservoir for releasing the active ingredient as a function of exposure to UV radiation, however.
There is therefore a need for sunscreen systems based on the traditional UVB absorbing aromatic compounds as well as newer compounds, which provide for long term protection, and actually has an increasing PI as a function of exposure to UVB, solar radiation or at least on environmental condition, in general.
Furthermore, there is a need to include such self dosing sun blocking agents in other cosmetic preparations such as make up, lipsticks, various creams and emollients. There is also a need for cosmetic preparations in which fragrances, dyes or antiperspirants are discharged as a function of exposure of the preparations to solar radiation and other environmental conditions.
The inventors have surprisingly found that encapsulating active ingredients for the skin, within capsules whereby the capsules"" wall material deteriorates with exposure to the elements, and particularly to the UV part of the solar spectrum, provide a continuous mechanism for replenishing a film of UV absorbing agent or other active ingredients onto the skin.
A preferred embodiment of the invention includes a spectrum of capsules, differing in wall deterioration characteristics, so that some of the capsule walls deteriorate rapidly, while others deteriorate slowly so as to provide, with exposure to the elements and UV flux from the sun, a PI that increases with exposure, or in essence a xe2x80x9cself dosingxe2x80x9d sunscreen whereby the longer a person treated with the innovative sunscreen is in the sun, the higher the PI of the sunscreen, a feature heretofore not achieved in the prior art.
Accordingly, an object of the present invention is to provide means and methods resulting in sunscreens having a PI that increases with exposure to UV radiation in general.
It is another object of the present invention to provide a sunscreen in which the LTV absorbing agents are encapsulated in microcapsules having walls that are susceptible to UV degradation and subsequent release of the active ingredients.
It is another object of the present invention to provide a sunscreen in which the UV absorbing agents are encapsulated and the material of the encapsulating wall deteriorates with time due to natural degradation processes, such as exposure to humidity, oxygen in the air or light in general.
It is yet another object of the present invention to provide a sunscreen in which the active UV absorbing ingredients are encapsulated in microcapsules having walls that deteriorate with exposure to UV and other external natural agents at varying rates.
Accordingly a still further object of the invention is to provide a self dosing sunscreen composition and method for releasing sun blocking agent onto the skin of a user as a function of exposure to at least-one environmental condition over time. The environmental condition is preferably exposure to sun light, in particular, harmful UV radiation. The composition includes a medium adapted to be spread onto the skin of a user and a reservoir defining at least one wall for containing at least one sun blocking agent. The reservoir is dispersed in the medium and the wall is designed and/or selected to deteriorate over time with exposure to the environment condition or conditions, for releasing the sun blocking agent into the medium and onto the skin. At least one sun blocking agent is provided in the reservoir. The reservoir is preferably in the form of a multiplicity of microcapsules dispersed in the medium, each microcapsule having a wall and containing the at least one sun blocking agent, each wall deteriorating over time with exposure to the at least one environmental condition for opening the microcapsule to release the agent.
A still further object of the invention is to provide self dosing cosmetic or other preparations and compositions, and methods for releasing fragrances, antiperspirants, dyes, cooling/warming agents, flavors, insect repellents, antibacterial agents, hair conditioners, self tanning agents and/or other active ingredients onto the skin of the user, as a function of exposure to a least one environmental condition over time. The environmental condition is preferably exposure to sunlight. The composition includes a medium adapted to be spread onto the skin of a user, and a reservoir defining at least one wall for containing at least one fragrance or antiperspirant or cosmetic dye, or any other active ingredient. The reservoir is dispersed in the medium and the wall is designed and/or selected to deteriorate over time with exposure to the environmental condition or conditions, for releasing active ingredient or active agent into the medium and onto the skin. At least one ingredient or agent is provided in the reservoir. The reservoir is preferably in the form of a plurality of microcapsules dispersed in the medium, each microcapsule containing the at least one ingredient or agent and the walls of the microcapsules deteriorating over time with exposure to the at least one environmental condition, such deterioration resulting in the release of the ingredient or agent.